sequentially

Declare asynchronous operations sequentially in CooffeeScript

This module allows writing deeply-nested asynchronous code in CoffeeScript in a sequential manner.

This is intended to be used from CoffeScript, as it takes advantage of that language's syntax. Other modules such as Async (async.series), Step or async-queue are probably a better match for JavaScript.

Steps to be executed sequentially are defined in a declarative manner:

sequentially = require 'sequentially'
sequentially ->
  @step (done) ->
    console.log "FIRST"
    done null, 1
  @step (value, done) ->
    console.log "SECOND: ", value
    done null, value + 1
  @step (value, done) ->
    console.log "THIRD", value
    setTimeout done, 2000, null, value
  @step (value, done) ->
    console.log "FOURTH", value
    done null
  @on_error (err) ->
    console.log "ERROR", err

Note the optional on_error function that will handle errors that occur at any point in the sequence.

Each step in the sequence should use its done parameter to execute and pass arguments to the next step.

The first argument passed to done should be not null to in indicate an error that will abort the sequence and execute the error handler.

Note that the function passed to sequentially is executed with this pointing to an special object. So, if you need to access the outer this you should assign it to a local variable:

sequentially = require 'sequentially'
self = this
sequentially ->
  @step (done) ->
    console.log "FIRST"
    self.f()
    done null, 1
  @step (value, done) ->
    console.log "SECOND: ", value
    done value + 1
  @step (value, done) ->
    console.log "THIRD", value
    setTimeout @next, 2000, null, value
  @step (value, done) ->
    console.log "FOURTH", value
    done
  @error (err) ->
    console.log "ERROR", err

Or, since version 2.1, you can simply use the scope options that defines the this value with which the steps are executed:

sequentially = require 'sequentially'
sequentially (scope: this) ->
  @step (done) ->
    console.log "FIRST"
    @f() # 'this' has the same value as in the outer scope
    done null, 1
  @step (value, done) ->
    console.log "SECOND: ", value
    done value + 1
  @step (value, done) ->
    console.log "THIRD", value
    setTimeout @next, 2000, null, value
  @step (value, done) ->
    console.log "FOURTH", value
    done
  @error (err) ->
    console.log "ERROR", err